Phototube



June 20, 1939. M. c. TEVE)S -r AL 5 9 PHOTOTUBE V Filed July 22, 1936 Z l u INVENTOR:

9 MART:N conneus TEVES AND FRANS MICHEL PENN1NG electrodes comprising an alkali metal layer ad- Patented June 20, 1939 PHOTOIUBE Marten Cornelis Teves and Frans Michel Pennng, Eindhoven, Netherlands, \assgnors to N. V. Philips Gloeilampenfabreken, Eindhoven, Netherlands Application July 22, 1936, Serial No. 91,804 In the Netherlands August 5, 1935 electric layer on these parts does not or only slightly affects the sensitiveness of the cathode.

With a cathode having a concave active surface the anode may even be arranged behind the imaginary plane shutting off the interior surface of the cathode.

The novel features which we believe to be characteristic of our invention are set forth with particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection With the accompanying drawing in which Figure 1 is an elevation of a photo-electric tube made according to the invention, Figure 2 is a section of the cathode and the anode of Figure 1, and Figure 3 is a section of a modification of the electrode arrangement in Figure 1.

The tube in Figure l has a glass envelope l having sealed to it a stem 2 on which the cathode 3 is mounted. This cathode consists of a semicylindrical copper plate which is secured to the stem 2 by means of the supporting wires 4. One of these supporting wires 4 is provided With a supply conductor 5. The cathode is coated on the inner side with a photo-electric sensitive layer 6 consisting of a salt layer of caesium oxide to which a very thin caesium layer is adsorbed, the caesium oxide being mixed with silver particles and caesium particles. This photo-sensitive layer may be established by coating the inner side of the cop-per plate 3, before mounting the latter in the envelope, with a thin silver layer which, after the plate 3 has been mounted in the envelope and the latter has been exhausted, is oxidized for which purpose a small quantity of oxygen is introduced into the envelope and an electric discharge is brought about with the silvered copper plate 3 acting as a cathode. After removal of the oxygen, excess caesium is introduced into the envelope, this caesium reducing the silver oxido to caesium oxide which forms a mixture with the reduced silver. Moreover, caesium penetrates into this layer and a thin adsorbed caesium layer is formed on the caesium oxide layer.

The anode of the tube consists of two metal rods l which are mounted on the stem 2 and each of which is provided with a supply conductor 8. With normal operation of the tube these conductors are interconnected. As appears more particularly from Figure 2 the anodes 1 are positioned adjacent the edges and the outside surface of the photo-electric cathode and parallel with the axis of the tube. Since the anode rods 1 are located to one side of the cathode only part of the photo-electric surface is visible from the anode 4 Claims.

This invention relates to light sensitive electron dischar.ge devices of the gas type, more particularly to improvements in the electrode systems in such devices.

The gas-filling in such devices is used in order to obtain an amplification of the electron current emitted by the photo-electric cathode. The emitted electrons cause ionization of the gas in the tube, the pressure of the gas being such that the mean free path of the electrons is of the order of the distance between the electrodes, the free electrons and positive ions formed by ionization increasing the emitted electron current.

With the use in such tubes of photo-electric sorbed to a salt layer it often occurs that shortly after the tubes have been operated for the first time their sensitivity decreases, which entails serious practical difficulties.

The present invention has for its object to maintain the initial sensitivity of a light sensitive electron discharge device of the gas type.

According to the invention the anode is arranged in such a manner with respect to the cathode that the active surface of the cathode as viewed from the anode, is not visible or only partly visible. It has been found that the decrease in sensitivity can be avoided at least for the greater part by making the electric field distribution such that the number of positive ions formed upon ionization of the gas-filling and reaching thatpart of the cathode Which is exposed, is as small as possible. Thus, to obtain a long useful life of the tube the field distribution should not be rendered as uniform as possible, which was hitherto sought, but it should purposely be so chosen that the positive irons are drawn as much as possible to those parts of the cathode Which are not or only slightly exposed.

Such uneven field distribution is ensured in a simple manner by arranging the anode with respect to the cathode in the manner above referred to. The cathode may, for instance, be given a concave active surface in a known manner and for this purpose consist, for example, of a semicylindrical metal plate coated on the inner side With the photoelectric layer. In this case the anode may consist of two rod-shaped members which may be arranged on the outside of and on either side of the cathode and preferably parallel with the vertical edges of the cathode. Most of the lines of force emanating from the anode terminate at the edges of the cathode so that the positive ions mainly impinge on the marginal parts of the cathode. Deterioration of the photoand the lines of force emanating from the anode extend for the most part only to the marginal portions of the cathode.

The envelope is filled with gas such as argon at a pressure of 0.1 mm. During normal operation the inside or concave side of the cathode is exposed, the light rays falling for the most part on the central part of the photo-electric surface. The emitted electrons ionize the gas-filling and due to the low gas pressure the ions are princi pally formed in the vicinity of the anode. These ions follow the lines of force emanating from the anode, so that the greater number of the positive ions reach the cathode in the vicinity of its edges.

If desired, the anode rods 1 may be interconnected at the upper end Furthermore, it is possible to locate the anode rods l exactly opposite the edges of the cathode Figure 3 represents another arrangement of the anodes relatively to the cathode. In this figure the anode rods l may be arranged completely behind the imaginary plane 9 passing through the edges of the cathode and shutting off the inner or concave surface of the cathode. In this case a great part of the positive ions Will reach the cathode at the back, where they cannot deteriorate the layer.

While we have indicated the preferred embodiments of our invention of which We are now aware and have also indicated only one specific application for which our invention may be employed, it will be apparent that our invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed without departing from the scope of our invention as set forth in the appended claims.

We claim:

1. A phototube having an envelope containing a gas filling, a cathode having a concave surface, a light sensitive coating on said concave surface and an anode positioned adjacent to but outside of the region formed by the orthogonal projection from the concave surface of said cathode.

2, A phototube having an envelope containing a gas filling, a semi-cylindrical cathode within said envelope and coated on its inside surface with a light sensitive coating, a rod-like anode positioned adjacent and parallel to a longitudinal edge of said cathode but on the outside of the concave surface of said cathode and the region formed by the orthogonal projection from the concave surface of said cathode.

3. A phototube having an envelope containing a gas fi1ling, a semi-cylindrical photocathode within said envelope, a light sensitive coating on the inner surface of the photocathode and a pair of anode rods each of said rods positioned parallel and adjacent to a longitudinal edge of said photocathode but on the outside of the concave surface of said photocathode and the region formed by orthogonal projection from the concave surface of said cathode.

4. A phototube having an envelope containing a gas filling, a semi-cylindrical photocathode within said envelope, a light sensitive coating on the inner surface of said cathode, and a pair of rod-like anodes, each of said anodes positioned parallel to and adjacent a longitudinal edge of said cathode and on the outside of and adjacent the convex surface of said photocathode, the active coating as viewed from said anodes not being visible.

MARTEN CORNELIS TEVES. FRANS MICHEL PENNING. 

